The invention relates to a medical instrument, especially for use in surgery, comprising two parts which can be joined to each other by means of a coupling, a coupling sleeve which is joined to one of the two parts of said instrument, and a coupling shank which is formed on the other part of the instrument and can be fixed inside the coupling sleeve, where the coupling sleeve and the coupling shank can be joined to each other in a non-positive fit by at least one coupling element arranged inside a guide cage, and where the coupling element can be moved in an essentially axial manner only, and where the coupling is provided with only one spring element.
A medical instrument of this type is, for instance, known from DE-A1 43 41 736. In this known instrument, the coupling shank is fixed on the grip, or on the sleeve, by means of a ball used as coupling element, which when engaged is inserted into a recess of the coupling shank. Thanks to this structure, the entire axial force applied on the instrument and by the instrument must be transmitted by means of the ball used as coupling element. This results in extreme pressure on the recess of the coupling shank as well as a transverse loading of the ball on two closely adjacent points on the spherical surface.
Another medical instrument is, for instance, known from DE-A1 195 14 098 submitted by the applicant. In this instrument designed in the form of a tube shank instrument, the two parts of the instrument are fixed together by means of a recess formed in the coupling shank which is inserted into the coupling sleeve. The coupling element designed in the form of a ball is inserted, in engaged position, into said recess under compressive load of a first spring. To release this connection, the coupling sleeve is designed as a turn sleeve which can be pivoted around the longitudinal axis of the tube shank instrument. A second spring, i.e. a torsion spring, is arranged inside the turn sleeve and counteracts the rotation. Although the coupling of this medical instrument secures a secure joining of both parts of the instrument to one another, the diameter of said instrument is large, partly because of the design of the turn sleeve, so that an instrument of this type is too big and awkward for use in the HNO area, for instance. In addition, the manufacture of the coupling for said instrument is quite expensive because of the use of the two springs, among other reasons.
Other medical instruments comprising rapid couplings are known, for instance, from DE-A1 39 34 610, U.S. Pat. No. 4,403,959 and from U.S. Pat. No. 4,577,875. The disadvantage of all these instrument couplings is that, first, they have a large diameter and, second, they require at least two spring elements in order to ensure a joining of both parts of the instrument parts to one another without vacant space. Because of this type of structure, the known medical instruments comprising rapid couplings are quite costly.
Because of this state of the art, it is the objective of the present invention to provide a medical instrument of the aforementioned type, which ensures a joining of both parts of the instrument to one another that is essentially free from play, and whose structure is simple and cost-effective as well as slender in design.
The solution to this objective by the invention is characterized in that the coupling element abuts onto oblique contact members of coupling sleeves and coupling shank, and the angle (alpha) between the center axis of the coupling sleeve and the oblique contact member of said coupling sleeve is larger than the angle (beta) between the center axis of the coupling shank and the oblique contact member of said coupling shank.
In the instrument in accordance with the present invention, the force generated by inserting the shank into the coupling sleeve is absorbed by the contact members. On the other hand, the coupling is automatically engaged because of the different inclination of the oblique contact member when pulling out the shank. The ball is compressed in its entirety over two nearly opposite points on the spherical surface and is brought into contact with the oblique contact members of the coupling sleeve and coupling shank, resulting in minimal wear and tear. This structure of the coupling comprising both oblique contact members and the coupling element arranged between said oblique contact members facilitates a simple compensation of manufacturing tolerances, since no precise engagement position is defined in contrast to the technique of DE 43 41 736 A1. Therefore, the coupling in accordance with the present invention facilitates the transmission of great forces and momentum, and simultaneously ensures secure linkage of the coupling elements.
In addition, the invention calls for the attachment of a slider on the outside surface of the coupling sleeve, where said slider is adjustable in the axial direction of said coupling sleeve and engaged with the guide cage for at least one coupling element. At least one coupling element is slidable by means of this slider and also engages with the oblique contact member of the coupling shank. The use of the slider which can move in the axial direction of the coupling sleeve facilitates a considerable reduction of the diameter of the coupling in comparison with the couplings of the instruments defined by current technology. Moreover, the slider is simple in construction, which in turn lowers the cost of manufacture of a medical instrument in accordance with the invention.
In a practical embodiment of the present invention, it is proposed that the slider and the guide cage are joined together by clamping or in a non-positive fit for at least one coupling element over at least one retaining member. The axial movement of the slider is transmitted over said retaining member to the guide cage of the coupling element in such a way that the shifting of the slider against the force of a compression spring under compressive load brings the coupling element into an engaged position so that at least one coupling element released from the oblique contact member of the coupling shank can be engaged.
In order to avoid a twisting of both parts of the instrument against one another, the present invention proposes a mounting of a protection against torsion between both instrument parts.
In accordance with a first practical embodiment of the present invention, the protection against torsion is designed as a pivot arranged in one of the instrument parts, which engages in a corresponding groove of the other instrument part.
In accordance with a second embodiment of the present invention, the pivot in one of the two instrument parts can be engaged in one of several grooves of the other instrument part. This arrangement makes it possible to secure the instrument parts to one another at various angles.
In accordance with another embodiment of the present invention, the instrument parts can be joined to one another at various angles because the protection against torsion is designed in the form of an engagement mechanism acting between the instrument parts.
A particularly great freedom of play between both parts of the instrument to be joined together can be obtained if the coupling shank over its peripheral area is in contact with two contact members located on the inner side of the coupling sleeve, where the distance between said contact members is several times greater than the diameter of said coupling shank as seen in the axial direction of the coupling shank. Furthermore, the greater distance between the contact members prevents the high maximum torque to the other part of the instrument that occurs with known instruments.
In accordance with a practical embodiment of the present invention, one of the two contact members is conical. It is also proposed, in accordance with the invention,
For use of an inventive medical instrument as a tube shank instrument, one part of the instrument has a handle comprising a fixed handle part and a pivotal handle part arranged opposite to said fixed handle part. The other instrument part is provided with a push/pull rod arranged in the coupling shank provided for use of a medical gripping instrument.
With this refinement, the medical instrument in accordance with the present invention is characterized in that a retaining member is arranged on the proximal end of said push/pull rod which can be fixed in a triggering element that is slidable in the axial direction of said handle part.
In accordance with a preferred embodiment of the present invention, the retaining member on the proximal end of the push/pull rod is designed as a ball which engages in a complementary ball socket in the manipulating element.
Finally, the present invention proposes a pivot-groove control between the pivotal grip of the handle part and the manipulating element axially slidable in said handle part, and which is used for shifting the push/pull rod.